1. Field of the Disclosure
The present disclosure relates to fiber laser systems operative to controllably align a beam. More specifically, the present disclosure relates to a system and method for adjustment of beam switches and fiber-fiber couplers using a reflecting element.
2. Discussion of Relevant Art
One of important parameters of fiber laser systems (FLS) is beam quality at the output of the system. The beam quality is a “measure of how tightly a laser beam can be focused under certain conditions (e.g., with a limited beam divergence)” from the Encyclopedia of Laser Physics and Technology, 2008. Conventionally, one of the quantifying factors of the beam quantity is “the beam parameter product (BPP), i.e., the product of beam radius at the beam waist with the far-field beam divergence angle” Encyclopedia of Laser Physics and Technology, 2008. The optimization of the BPP depends upon, among other factors, the configuration and “correct” location of optical component guiding an incident beam toward a surface to be treated.
Referring now to FIG. 1 there is an illustration of an exemplary fiber laser system 10 having a modular configuration so that at least some components of the system can be disconnected from the rest of the system, if a need arises. The FLS 10 includes a fiber laser 12 generating a laser output, which is coupled into a feeding fiber 14, a delivery system 16, such as a beam switch (BS) or fiber-fiber coupler (FFC), a processing fiber 18 guiding the laser output which is coupled into an end tool 21, such as a laser head.
The delivery system 16 is configured with input and output connectors supporting feeding and processing fibers, respectively. The input connector is fixed to the upstream face of delivery system 16, whereas the output connector is removably mounted to the downstream face and receives a laser output beam through a few, discrete light guiding/focusing optical components of system 16.
In use, the laser output is delivered to laser head 21 configured to process materials. As known to an artisan, laser systems, like system 10, are most efficient when the optical power is concentrated inside the core of processing fiber 18. The optical misalignment between feeding and processing fibers 14 and 18, respectively, which often happens during assembling and/or reassembling FLS 10, leads to the coupling of part of the laser light into the cladding of the processing fiber 18. As a consequence, the BPP of the output light is not minimally optimal and the proper alignment should be reestablished.
As the cladding-guided light propagates along a light path, it is typically partly backreflected. At a certain level, the backreflected light, when detected by fast fiber beam detectors (FFBD) 24, which are mounted to the housing of the delivery system 16, can serve as a reliable indication of proper alignment. Indeed, power of light coupled into the cladding is the power of light not coupled into the core and thus lost at the output of system 10.
The system 10 is being tested and tuned up at a manufacturing facility by using a stationary beam-quality control device 22 operative to determine the minimal value of BPP. The minimal value of the BPP corresponds to a certain position of actuators operative to controllably displace an outer connector 25 which supports processing fiber 18 and is displaceably mounted to the housing of delivery system 16. The optimal position of the actuators means that FFBD 24 should detect deviation of laser beam which, instead of getting coupled into the core of fiber 18, is incident upon the cladding thereof. Having coupled into the cladding, cladding light reflects back and is picked up by FFBD 24. If the backreflected light is within the norm, system 10 continues to operate. Otherwise, the system should be shut down.
Once adjusted, system 10 without, of course, beam-quality control device 22, is delivered to an end user. When the actuators are displaced to the predetermined position in the field, FFBD 24 may malfunction for the reasons explained below and generate a minimal signal that does not correspond to the minimal power loss and optimal BPP. The process fiber 18 has a structure allowing for minimal losses including those in the cladding which cause the decreasing of the scattered light and, therefore, inadequate operation of detectors 24.
This is particularly relevant to the fiber configuration having a cladding which is capable of guiding light; such a configuration may include, but not limited to a multi-cladding fiber widely used in high-power fiber laser systems. Since a cladding typically does not have a heat-absorbing element, the light supported in the cladding may be powerful enough to thermally damage the fiber. In this case, the FFBd sensors 24 do not work properly because there is no back-reflected light from the cladding. Furthermore, FFBD detectors 24 may be mounted to the housing of delivery system 16 such that they are shielded by other parts. As a consequence, delivery system 16 may not properly operate which is turn leads to the misalignment of the optical components.
A need, therefore, exists for a reliable alignment system allowing for the factory-established settings to be easily reproduced when a fiber laser system is in use.